The invention concerns a device for controlling the ventilation of an internal space, particularly in motor vehicles, as a function of signals of a pollutant sensor essentially subjected only to external air, having switch-over between air supply operation and air recirculation operation depending on the pollutant concentration.
Generally speaking, fresh air from outside should be continuously supplied to the passenger compartment of motor vehicles during the journey in order to avoid the possibility of the carbon dioxide content in the air increasing excessively in the internal space due to the breathing of the people in the internal space and leading to tiredness symptoms among those travelling. In addition, the moisture content of the air in the internal space would also increase in an undesirable manner without the supply of fresh air.
On the other hand, it is often useful to stop or switch off the supply of fresh air, i.e., the "air supply operation" and therefore to switch to "air recirculation operation" in which the air in the internal space is only circulated around by convection or by a fan.
The switch-over from air supply operation to air recirculation operation generally takes place in motor vehicles by means of an air butterfly which, in its air supply position, connects the inlet end of a fan (whose outlet end is connected to the internal space) to an external air connection and, in its air circulation position, connects it to an internal space connection.
In this connection, it is known to undertake the switch-over between air supply operation and air recirculation operation automatically as a function of the signals from a pollutant sensor which is subjected to external air and generates signals which are correlated with the pollutant concentration in the external air.
It is also known from German Patent Document 37 31 745 to continuously record the signals from the external air pollutant sensor and to determine from them a continually updated average value for the external air pollutant concentration. This average value is used as the reference value for a comparison with the current actual value of the external air pollutant concentration. If the current actual value indicates an actual pollutant concentration which exceeds the average or reference value for the pollutant concentration by a specified amount, air recirculation operation is switched on. Otherwise, air supply operation takes place. This known method of control is not satisfactory because the pollutant concentration of the internal air cannot be taken into account at all. In particular, the fact that the air in the internal space can deteriorate substantially during long periods of air recirculation operation is ignored with the result that the quality of the internal air can finally be lower than the possibly relatively poor quality of the external air. No account is taken of this, however, in the decision between air supply operation and air recirculation operation.
From German Patent Document 35 26 462, it is known to arrange a pollutant sensor for the external air, on the one hand, and a pollutant sensor for the internal air, on the other, in order to decide, by comparing the pollutant concentrations determined in the external air and the internal air, whether air supply operation or air recirculation operation is more advantageous in terms of the quality of the internal air and which at these operations should, therefore, be switched on.
It is not possible to achieve such arrangements in practice or at least not at a justifiable expense. This is mainly due to the fact that the signals of conventional pollutant sensors are affected by very many parameters and not just the pollutant concentration in the surroundings of the particular sensor. Conventional pollutant sensors exploit the effect that typical air pollutants, such as the oxides of carbon and nitrogen, penetrate to different amounts into electrically conductive ceramic bodies as a function of their concentration in the air and therefore change the electrical resistance of the ceramic body. This effect depends greatly on temperature. In order to have the electrical resistance values change sufficiently clearly with fluctuating pollutant concentration, the ceramic body must be held at a relative high operating temperature by means of a heating element. Even so, markedly different surface temperatures can occur on the ceramic body depending on whether the ceramic body is subjected to very cold or warm air and whether or not the air has a high flow velocity relative to the ceramic body. In addition, the surface temperature of the ceramic body and the ability of the pollutants to penetrate into the ceramic body are also modified by the humidity of the air, which may very greatly under certain circumstances. The result of this is that pollutant sensors installed at different positions can also generate markedly different signals even when the concentration of the pollutants being monitored is the same in the vicinity of both sensors. On the other hand, equal signals from pollutant sensors installed at different locations by no means indicate that the pollutant concentrations at the different locations are also equal. It follows that the signals of two sensors located at different positions cannot be compared directly.
A comparison between the signals of the pollutant sensor for the external air and the signals of the pollutant sensor for the internal air would therefore only be possible if account is taken of the different environmental influences on the two sensors. Although this could theoretically be done, it is not practical. In the case of motor vehicles, a comparison is further complicated by the fact that extraordinarily large changes in the air temperature, the air humidity and the flow velocity of the air can occur both in the external space and in the internal space. Furthermore, other parameters have to be taken into account in addition to those just mentioned if the signals of two sensors are to be compared.
An object of the invention is to provide a practical device which takes account of both the quality of the external air and the quality of the internal air in the control of the ventilation of an internal space.
This and other objects are achieved in a device for controlling the ventilation of an internal space of a motor vehicle by means of a computer--and taking account of the sensor signals of the pollutant sensor for the external air, the current mode of operation--air supply operation or air recirculation operation--and specified experience values which can be called up--a first quantity correlated with the pollutant concentration in the internal space is determined and is compared with a second quantity correlated with the pollutant concentration in the external air and derived from the sensor signals, and that either air supply operation or air recirculation operation is switched on or retained depending on the result of this comparison.
The invention is based on the general idea that appropriate tests performed by one of ordinary skill in the art make it possible to determine "experience values" for a tendency of the air quality in the internal space to deteriorate with air recirculation operation and for a delayed and/or weakened equalization between the air quality in the internal space and the air quality of the external air occurring in the case of air supply operation. If these experience values are called upon by the computer, it is immediately possible to determine values for the quality of the internal air by computation --i.e. by computer simulation--from the sensor signals of the pollutant sensor for the external air, i.e. from signals which reproduce the quality of the external air.
The invention therefore uses the fact that the computer "knows", on the basis of the experience values which it can call upon, how the fresh air introduced into the internal space in the case of air supply operation mixes with the air present in the internal space and therefore equalizes, with a delay, the air quality in the internal space and the air quality in the external space and how the quality of the air in the internal space deteriorates with air recirculation operation relative to the condition at the beginning of the air recirculation operation due to the breathing of the occupants.
On the one hand, therefore, the invention takes account of the fact that the quality of the air in the internal space depends markedly on the quality of the air in the external space. On the other hand, the typical deviations of the quality of the air in the internal space from the quality of the air in the external space can be determined by means of the computer because the latter has access to corresponding experience values.
Because the signal reproducing the quality of the air in the internal space is generated by means of the computer, it is immediately possible to ensure that the signal for the quality of the internal air is formed or structured corresponding to the signals reproducing the pollutant concentration of the external air and represents a fictitious external air pollutant concentration at which the current quality of the internal air remains unaltered.
For this purpose, the experience values for the deviation of the quality of the internal air from the quality of the external air only need to be formed as factors (dependent on time and operating condition) with which the value or the corresponding signal reproducing the external air quality is associated as a mathematical product.
The computer therefore only has to have access to corresponding time-dependent factors in order to determine, by product formation, a signal for the internal air quality from the signal for the external air quality.
With respect to high measurement accuracy--and not only in the method according to the invention and the device according to the invention--it is desirable for the pollutant sensor for the external air to be arranged so that it is protected against air draughts and dripping water in a chamber whose walls--at least in some areas-- are permeable to gases and to the pollutants which have to be monitored.
It is then useful for one wall area to be closed by a gas-permeable membrane; the other wall areas are, in contrast, gas-tight and liquid-tight. A mat may, if appropriate, also be used instead of a membrane.
Because of this arrangement, the pollutant concentration in the chamber changes practically simultaneously with the pollutant concentration in the external air. It is, however, advantageous to avoid the pollutant sensor being subjected, because of different travelling speeds or variable weather, to air flowing at different speeds and/or spray water or mist droplets and producing greatly varying signals due only to a change in these parameters.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.